
Clock-Synchronous Serial I/O
Mitsubishi microcomputers
M30201 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
258
2.5.3 Operation of the Serial I/O (transmission in clock-synchronous serial I/O
mode, transfer clock output from multiple pins function selected)
Note: This can be selected only when UART0 is used in combination with the internal clock.
(1) Setting the transmit enable bit to “1” makes data transmissible status ready.
(2) When transmission data is written to the UART0 transmit buffer register, transmission data
held in the UART0 transmit buffer register is transmitted to the UART0 transmit register in
synchronization with the first falling edge of the transfer clock. At this time, the first bit of the
transmission data is transmitted from the TxD0 pin. Then the data is transmitted bit by bit from
the lower order in synchronization with the falling edges of the transfer clock.
(3) When transmission of 1-byte data is completed, the transmit register empty flag goes to “1”,
which indicates that the transmission is completed. The transfer clock stops at “H” level. At
this time, the UART0 transmit interrupt request bit goes to “1”.
(4) Setting CLK/CLKS select bit 1 to “1” and setting CLK/CLKS select bit 0 to “1” causes the
CLKS pin to go to the transfer clock output pin. Change the transfer clock output pin when
transmission is halted.
Operation
In transmitting data in clock-synchronous serial I/O mode, choose functions from those listed in Table
2.5.2. Operations of the circled items are described below. Figure 2.5.8 shows the operation timing, and
Figures 2.5.9 and 2.5.10 show the set-up procedures.
Table 2.5.2. Choosed functions
Item
Set-up
Transfer clock
source
Internal clock (f1 / f8 / f32 / fc)
External clock (CLK0 pin)
CLK polarity
Output transmission data at the falling edge of the transfer clock
Output transmission data at the rising edge of the transfer clock
O
Transmission
interrupt factor
Transmission buffer empty
Transmission complete
Output transfer clock
to multiple pins
(Note)
Not selected
Selected
O
Transfer clock
LSB first
MSB first
O